The deaths and injuries and furthermore damage to property caused by traffic accidents are to a substantial extent due to rear end crashes. It is to be admitted that in the last decades great progress has been made for the further development of passive protection against accidents, by which the consequences of accidents are reduced. In this respect it is only necessary to think of crumple zones, seat belts, head rests and airbags.
The development of brake lights which became known in the twenties has however hardly led to any significant step forward. Brake lights have only become brighter and somewhat larger and are turned on as soon as the brake pedal is moved a certain amount even without slowing down the vehicle. In the USA a center-mounted third brake light has recently been introduced.
The substantial disadvantages of known brake lights have however not been overcome by such improvements. Brake lights only shine on actuation of the foot brake and not whenever the vehicle coasts along, that is to say on deceleration because the driver takes his foot off the accelerator pedal or owing to switching on an additional engine or eddy current brake and furthermore not owing to the braking effect of the air. Such causes may lead to a deceleration both at a high speed (mostly owing to the resistance of the air) and at a low speed (mostly owing to the motor brake torque) of approximately 1.5 to 2 m/sec.sup.2. In the case of an unloaded truck simultaneous operation of the engine brake and an eddy current brake may lead to deceleration values of even up to 3 m/sec.sup.2, this all taking place without operating the light. Such deceleration is as such equal to 15 to 30% of an emergency braking effect under dry road conditions and approximately 50 to 100% of the deceleration during emergency braking on a snow covered road surface. Therefore even by removing one's foot from the accelerator pedal for a time of several seconds a speed differential in relation to the vehicle behind is established, which involves the danger of a rear end collision without the brake light being turned on. This is something which has special serious effect in all those cases in which the actual braking operation (with the brake light) is preceded by an extended coasting phase (without the brake light). It is specially that when a sufficient safety distance is maintained that the deceleration without the brake light turned on which is hardly noticed by the eye, since at a considerable distance three-dimensional vision is practically non-existent. Furthermore the optical effect of an object becoming larger (that is to say in the case of the vehicle in front) on drawing closer is at a minimum at a great distance apart, and since for instance in the case of a distance of 100 meters drawing closer by 10 meters only causes an increase in apparent size of 11%: in the case of a distance of 20 meters drawing closer by 10 meters will practically double the apparent size of the preceding vehicle.
Owing to absence of early warning valuable time is "squandered" at the start of the required braking of the following vehicle, since the braking path "wasted" is much longer at high speed. An early warning effect for great distances is however now way achieved by a conventional brake light.
A further disadvantage of a customary brake light is due to the fact that the warning caused by the light being turned only continues as long as braking is taking place or, respectively, the brake pedal is depressed. However by no longer braking the danger of a rear end collision is not banished, since the speed differential in relation to the following vehicle owing to the braking operation is still present. On being turned off the brake light creates the erroneous impression in fact that the danger no longer exists.
A further disadvantageous effect is that the intensity of the warning in the case of conventional brake lights is independent from the degree of the braking deceleration. This may on the one hand be responsible for a panic reaction (for example sharp braking without the safety distance being sufficient) and accordingly for an effect causing an accident: on the other hand there is however not the sufficiently increased intensity of the warning, which would for instance be necessary in the case of emergency braking with a high deceleration effect.
For around 20 years the so-called warning blinking system has been prescribed by law (in Germany). In this respect it is a question of a manual switching on of all four direction indicators, which are then turned on and turned off synchronously. Operation is prescribed for securing stationary vehicles on high speed roads (for example in a traffic jam) or when a vehicle is being towed away. It is more or less a question of a permanently turned on braking light which has proved highly successful in practice, since it will be turned on by an experienced driver on high speed roads just when he sees a jam or an accident from a distance. The disadvantage of a warning blinking system is however that it must be operated by hand and specially in the case of emergency braking, that is to say a particularly serious danger, there is no time for its operation and the driver should not have his attention diverted by having to operate additional equipment. Even after a rear end collision many drivers are shocked or physically injured and not in a position to switch on the warning blinking system.
Many experienced drivers warn the following traffic by intermittently braking and by intermittent operation of the brake lights (if the brake pedal is eased off sufficiently). This method does however suffer from the substantial disadvantage that it is only applicable in the case of a low braking deceleration and a sufficiently long time, and is not however applicable if there is a real danger to be feared and a powerful braking action is called for.
A further development, which has been subject to much developmental work without however producing any substantial success, is proximity radar, which when the following vehicle does not keep to the required safety distance, an optical or acoustic signal is produced in such following vehicle or even an action is produced automatically braking the following vehicle. The disadvantages of proximity radar are manifold and are to be explained briefly as follows: an acoustic or optical warning (on the dashboard) is likely to be a distraction instead of an attraction of the attention in a reasonable manner, since it does not come from a point which is a source of the danger, i.e. the preceding vehicle, Furthermore such a radar system does not react to a speed differential, which is particularly dangerous, but rather only to a failure to maintain the safety distance. A further disadvantage is to be seen in the fact that the driver is much too frequently warned, that is to say for example even when a vehicle coming into his lane from another lane comes within the safety clearance or distance; in this case no additional warning is required, since the process of changing a lane is conspicuous and will be noticed even by a driver who is not particularly attentive. Furthermore an automatic application of the brakes or causing the engine to deliver less power by such proximity radar would be such an interference with driving that in many cases it might even be the cause of an accident.
Of recent times a suggestion has been made to cause a removal of the driver's foot from the accelerator pedal to turn on an orange "brake light" as a preliminary warning preceding the actual, red braking light. The advantage would then be that even deceleration due to dropping power would be indicated and if there were an immediately following braking operation the reaction time would be reduced by the time required for shifting one's foot to the brake pedal, i.e. a matter of some tenths of a second. The disadvantage of this system is that it responds to every removal of the driver's foot from the accelerator pedal, be it ever so short, and reduces the awareness of the following driver owing to too many events takings place simultaneously. Furthermore this circuit means that the number of rear end collisions is likely to be increased, since the braking operation as such turning on the red light is now not sufficiently distinct.
In a further development work has been aimed at shortening the response time of the brake lights, which normally amounts to 0.20 to 0.25 sec. This may be performed, for instance, by preheating the lamp filament with a low current or by the employment of LED's instead of incandescent lamps. In either case the response time may be shortened by around 0.10 to 0.15 sec, admittedly only a small step forward, since the braking distance at a speed of for instance 100 km/h is decreased by 3 to 4.5 meters and at 150 km/h is decreased proportionally thereto by 4.5 to almost 7 meters, The above described basic disadvantages of conventional brake lights are however not reduced or even overcome.
One object of the invention is consequently to provide a deceleration warning system and a method for the operation thereof, by which the danger of rear end collisions in road traffic or other movements is reduced and by which the disadvantages of the conventional brake lights and of warning blinking systems are prevented or reduced.